The present invention relates to electrodeless discharge lamps. In particular, the present invention relates to electrodeless discharge lamps in which a coil is provided inside a bulb.
Some discharge lamps are electrodeless discharge lamps that do not include electrodes. Since electrodeless discharge lamps do not include electrodes, they advantageously have a longer life than that of discharge lamps including electrodes that ends their life by depletion of an electron release material on the electrodes. The electrodeless discharge lamps emit light in an ultraviolet ray range or visible light range by the following operation. A high frequency alternating magnetic field, for example, from 50 kH to 50 MHz is generated by a coil, and luminous gases such as a rare gas, mercury, metal halide and the like enclosed in a bulb are excited by an induction field generated by the high frequency alternating magnetic field. The excitation of the luminous gas provides light emission in an ultraviolet ray range or a visible light range. Emitted light in an ultraviolet ray range can be converted to light in a visible light range by phosphors.
FIGS. 16A and 16B are schematic views showing the configuration of a conventional electrodeless discharge lamp. FIG. 16A is a cross-sectional view including the central axis of a core 1106, and FIG. 16B is a cross-sectional view taken along a line X-Xxe2x80x2.
Referring to FIGS. 16A and 16B, the configuration and the operation of the conventional electrodeless discharge lamp will be described. This conventional electrodeless discharge lamp is a lamp whose light is started and maintained by a high frequency alternating magnetic field generated in the vicinity of a coil, and is a (compact) self-ballasted electrodeless discharge lamp to which a lamp base 1101 is integrated.
The electrodeless discharge lamp shown in FIGS. 16A and 16B includes a lamp base 1101, a power source (not shown) disposed inside a power source portion 1102, and a translucent bulb 1104 in which a cavity 1105 is provided. A coil in which a winding 1103 winds around a cylindrical core 1106 is inserted in the cavity 1105. The lamp base 1101 and the power source in the power source portion 1102 are electrically connected to each other, and the power source and the winding 1103 are also electrically connected to each other. In FIG. 16A, for clarification of the drawing, the vicinity of the central axis of the core 1106 and the lines of magnetic force (dotted lines) are shown in cross section, and the lamp base 1101, the power source portion 1102, the bulb 1104 are shown in their outlook.
When a commercial alternating current power is supplied to the power source (not shown) in the power source portion 1102 via the lamp base 1101, the power source portion 1102 converts the commercial alternating current power to a high frequency alternating current power, and supplies it to the winding 1103. The winding 1103 that has been supplied with the high frequency alternating current power forms a high frequency alternating magnetic field as shown by lines of magnetic force "ogr" in a space near the coil. When a high frequency alternating magnetic field is formed, an induction field orthogonal to the high frequency alternating magnetic field is generated, and then luminous gases in the bulb 1104 are excited and light is emitted. As a result, light in an ultraviolet ray range or a visible light range can be obtained.
However, the configuration of the conventional electrodeless discharge lamp shown in FIGS. 16A and 16B has the following problems. In the conventional configuration, the high frequency alternating magnetic field radiated from the coil as shown in the lines of magnetic force "ogr" leaks out from the bulb 1104, so that the magnetic field inside the bulb 1104 is reduced. As a result, the induction field formed by the magnetic field is reduced, which makes it difficult to start the lamp. In particular, when the ambient temperature is low, the startability of the lamp is significantly poor.
Therefore, with the foregoing in mind, it is an object of the present invention to provide an electrodeless discharge lamp with improved startability.
An electrodeless discharge lamp of the present invention includes a translucent bulb enclosing a luminous material; a coil for generating an alternating magnetic field that causes discharge in the luminous material; a power source for supplying an alternating current to the coil, the coil including a core and a winding provided near the bulb; and further includes startability improving means for improving startability of the lamp by generating a portion in which the alternating magnetic field generated by the coil is intensified in the bulb.
In one preferred embodiment, the coil is inserted in a cavity provided in the bulb.
In one preferred embodiment, the electrodeless discharge lamp further includes a phosphor applied onto the inner surface of the bulb.
In one preferred embodiment, the luminous material includes mercury and a rare gas.
In one preferred embodiment, the startability improving means is constituted by providing a high permeability member including a soft magnetic material near the core.
In one preferred embodiment, the high permeability member is provided in the bulb.
In one preferred embodiment, the high permeability member is a magnetic thin film provided on a surface of the bulb.
In one preferred embodiment, the high permeability member is plate-shaped and is inserted between the power source and the bulb.
In one preferred embodiment, the plate-shaped high permeability member has an asymmetric shape in which it is not symmetric with respect to the central axis of the core.
In one preferred embodiment, the plate-shaped high permeability member has a circular plate-like shape.
In one preferred embodiment, the center of the circle of the circular plate-shaped high permeability member is positioned in a portion other than the central axis of the core.
In one preferred embodiment, the high permeability member has such a U-shaped cross-section that the high permeability member surrounds the bottom of the bulb positioned on the side of the power source and a part of the side face adjacent to the bottom.
In one preferred embodiment, the high permeability member has at least one protrusion, recess or notch.
In one preferred embodiment, the startability improving means is constituted by the coil in which the winding density of the winding wound around the core is sparse on the side of the power source and is dense on the side opposite to the power source.
In one preferred embodiment, the startability improving means is constituted by the coil in which cross-section areas of the core are different along the central axis of the core.
In one preferred embodiment, the startability improving means is constituted by the coil provided with the core made of two or more magnetic materials having different magnetic permeabilities.
In one preferred embodiment, the electrodeless discharge lamp of the present invention is constituted as a self-ballasted electrodeless discharge lamp further including a lamp base electrically connected to the power source.
According to another aspect of the present invention, another electrodeless discharge lamp of the present invention includes a bulb made of a translucent material and filled with a luminous material inside the bulb; a coil including a core and a winding disposed near the bulb; and a power source for supplying a high frequency alternating current power to the winding. The electrodeless discharge lamp has a configuration in which discharge inside the bulb is caused by a high frequency alternating magnetic field formed by the coil, and the high frequency alternating magnetic field inside the bulb is distributed non-uniformly at the cross-section orthogonal to the central axis of the core.
According to another aspect of the present invention, yet another electrodeless discharge lamp includes a bulb made of a translucent material and filled with a luminous material inside the bulb; a coil including a core and a winding disposed near the bulb; and a power source for supplying a high frequency alternating current power to the winding. The electrodeless discharge lamp has a configuration in which discharge inside the bulb is caused by a high frequency alternating magnetic field formed by the coil, and the distribution of the high frequency alternating magnetic field inside the bulb is deviated to a direction opposed to the power source at a cross-section including a central axis of the core.
In one preferred embodiment, a magnetic member including soft magnetic material is provided near the core or integrally with the core.
According to another aspect of the present invention, a self-ballasted electrodeless discharge lamp of the present invention includes a translucent bulb enclosing a luminous material; an induction coil for generating an alternating magnetic field that causes discharge in the luminous material; a power source for supplying an alternating current to the induction coil; and a lamp base electrically connected to the power source. The induction coil includes a core and a winding provided near the bulb, and is inserted in a cavity provided in the bulb, a phosphor is applied onto an inner surface of the bulb, and a member including soft magnetic material is provided near the induction coil.
According to another aspect of the present invention, another electrodeless discharge lamp includes a translucent bulb enclosing a luminous material; an induction coil for generating an alternating magnetic field that causes discharge in the luminous material; a power source for supplying an alternating current to the induction coil; and a lamp base electrically connected to the power source. The induction coil includes a core and a winding provided near the bulb, and is inserted in a cavity provided in the bulb, a phosphor is applied onto an inner surface of the bulb, and the induction coil has a configuration that forms a dense portion in a distribution of the alternating magnetic field occurring in the bulb.
According to the electrodeless discharge lamp of the present invention, startability improving means for improving the startability of the lamp by producing a portion in which the alternating magnetic field generated by a coil is intensified in a bulb is provided. Thus, the startability of the lamp can be improved. In particular, the poor startability at low temperatures can be improved, so that an electrodeless discharge lamp that can be effectively used even under low temperature environments can be provided. In the case where the electrodeless discharge lamp of the present invention is constituted as a self-ballasted electrodeless discharge lamp, a commercial alternating current power can be supplied to the power source through the lamp case. Therefore, a lamp that is easy to handle can be provided.
The startability improving means can be constituted, for example, by providing a high magnetic permeability member including soft magnetic material near the core. Moreover, the startability improving means can be constituted by a coil in which the winding density of the winding wound around the core is sparse on the side of the power source and is dense on the side opposite to the power source. Furthermore, the startability improving means can be constituted by the coil having different cross-section areas of the core along the central axis of the core. In addition, the startability improving means can be constituted by the coil including a core made of two or more magnetic materials having different magnetic permeabilities.
This and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.